animateWithDuration问题

Question

Like many others I'm struggling with getting animateWithDuration to work. The code below is a little test I was trying to run. What I want todo is to add a UIView behind, fade the UIView on top and then remove it. The problem is that the fade animation doesn't last the entire 10 second length (it actually completes instantly) despite the completion block executing 10 seconds later as desired.

Does anyone have any ideas what I'm doing wrong. I'm a beginner so I'm sorry in advance if I'm overlooked something very simple.

Thanks!

import UIKit

class ViewController: UIViewController {

    @IBOutlet  var graphView: UIView!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        graphView.addSubview(createView(UIColor.greenColor()))
    }

    func createView(color: UIColor) -> UIView {
        let viewToReturn = UIView(frame: CGRectMake(0, 0, 320, 354))
        viewToReturn.backgroundColor = color
        return viewToReturn
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    @IBAction func zoomIn() {

        let viewToRemove = graphView.subviews[0] as UIView

        graphView.addSubview(createView(UIColor.redColor()))

        UIView.animateWithDuration(10.0, animations: {
                println("Runs")
                viewToRemove.alpha = 0.0
            }, completion: {(bool) in
                if bool {
                    viewToRemove.removeFromSuperview()
                    println("End")
                }
        })

    }

}

Answer 1

You are adding the new subview on the top of the old subview . When you call addSubView function, the new subview is added on top of the old. This is why the the animation change is not visible. Try adding

self.view.bringSubviewToFront(viewToRemove)

before starting the animation.

Or you can directly add your new subview below the old using.

self.view.insertSubview(createView(UIColor.redColor()), belowSubview: viewToRemove)